Composition comprising metallocene plastomer and ethylene/alkyl (meth) acrylate polymer with their secant moduli ratio greater than 1

ABSTRACT

The invention concerns a composition comprising an ethylene/alpha-olefin metallocene copolymer and an ethylene/alkyl (meth)acrylate radical copolymer, the ratio of their secant moduli being greater than 1. The invention also concerns films obtained from said composition, in particular a stretchable adhesive film, and a high temperature extrusion method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application of InternationalApplication No. PCT/FR98/01696, which was filed on Jul. 30, 1998, andwhich published in French on Feb. 11, 1999, which in turn claimspriority from French Application No. P 97/09859, which was filed on Aug.1, 1997.

BACKGROUND OF THE INVENTION

The present invention relates to a novel composition of metalloceneplastomer and ethylene/alkyl (meth)acrylate copolymer, and to objectsobtained therefrom.

Copolymers of ethylene and alpha-olefin obtained by single-sitemetallocene catalysis are known. As these copolymers are homogeneous incomposition, it has been possible to prepare products having a densitycomprised, for example, between 0.905 and 0.880 g/cm³, known asplastomers, having good mechanical and optical properties. The moleculardistribution of such plastomers is very narrow and is characterized by apolydispersity index (ratio I=Mw/Mn) which is low, in general I<3.

Consequently, if such plastomers have good mechanical and opticalproperties, their rheology makes them poorly suited to implementation byextrusion or injection molding, because of the followingcharacteristics:

high specific energy due to elevated viscosity at the shearing gradientsof extrusion screws;

tendency to extrusion faults;

instability of the molten material leaving the die due to poorelongational viscosity.

One consequently looks for means of modifying the rheological behaviorof such ethylene metallocene (plastomer) copolymers while stillpreserving their mechanical and optical properties.

Several documents disclose modification of certain ethylene/alpha-olefin(co)polymers through mixing with other (co)polymers.

U.S. Pat. No. 3,176,052 discloses homogeneous mixtures comprising, byweight, (a) 25 to 95% ethylene/alpha-olefin copolymer obtained byZiegler-Natta catalysis having a density higher than 0.92 g/cm³ and anMFI comprised between 0.1 and 10 dg/min, which is heterogeneous incomposition, and (b) 75 to 5% of a radical polyethylene having a densitycomprised between 0.91 and 0.94 g/cm³.

U.S. Pat. No. 4,623,581 discloses a homogenous mixture comprising, byweight, (a) 25 to 98% ethylene/alpha-olefin copolymer which isheterogeneous in composition with a density between 0.905 and 0.940g/cm³ and an MFI comprised between 0.4 and 3 dg/min, and (b) 75 to 2% ofa radical polyethylene having a density comprised between 0.91 and 0.94g/cm³, which has a polydispersity index above 4, said polymer havingspecific properties of crystallinity and alpha-olefin monomerdistribution. The radical polyethylene according to that patent can bean ethylene copolymer with up to 20% by weight of an alkyl acrylate, forexample, 17.5% by weight butyl acrylate. There is no mention in thisdocument of the improvement to rheological properties of the modifiedpolymers; further, this is not the intended aim. This patent alsoindicates that these modified ethylene polymers do not have apolydispersity index comprised between 2.7 and 4.1 (by making referenceto European patent application 0,006,110); these modified ethylenepolymers consequently have a satisfactory rheology which does not needto be modified.

European patent Application 0,006,110 discloses a mixture comprising, byweight, (a) 80 to 99% of ethylene/alpha-olefin copolymer having apolydispersity index comprised between 2.7 and 4.1 and (b) 20 to 1% of ahigh pressure low-density homopolyethylene, the addition of low densityPE being intended to overcome the defective rheology of theethylene/alpha-olefin copolymer.

International Application WO-A-9507314 discloses packagings obtainedfrom substantially linear ethylene/alpha-olefin copolymers having lowpolydispersity indexes, for example comprised between 1.5 and 2.5. Thispatent discloses the addition of several types of film propertymodifiers, including rheology modifiers, while also indicating that theethylene/alpha-olefin copolymers are preferably employed alone. Themodifiers indicated in the description include LDPE, EVA, EVOH, PB, HDPEand LLDPE. The example given in that patent mentions LDPE or a linear EPcopolymer as rheology modifier. However, such rheology modifiers havevery high moduli, and consequently do not allow industrial production offilm having adequate properties. Another possible modifier according tothat document is an EVA; nevertheless, this modifier cannot be extrudedat a sufficiently high temperature as it degrades at temperatures of220° C. or even lower.

U.S. Pat. No. 5,326,602 discloses compositions comprising an ethylenepolymer with an ethylene/acrylate copolymer. The ethylene polymer isobtained by Ziegler-Natta catalysis and does not have a narrow moleculardistribution. Additionally, that patent does not disclose the action ofethylene/acrylate copolymer on the processability of an ethylenepolymer.

U.S. Pat. No. 5,593,747 discloses compositions comprising a particularmetallocene ethylene polymer, intended for the manufacture ofheat-shrinkable films. In that patent, this metallocene polymer can bemixed with a thermoplastic polymer. However, the only examples givencover addition of EVA.

European Patent Application 0,597,502 discloses compositions comprisinga metallocene ethylene polymer having a density of at least 0.900 g/cm³,also intended for manufacture of heat-shrinkable films. In that patent,this metallocene polymer can be mixed with a thermoplastic polymer ofthe radical ethylene copolymer type. Although ethylene/acrylatecopolymers are specifically mentioned, the only examples cover theaddition of EVA.

In fact, adding EVA to a metallocene polymer does not make it possibleto improve processability. Additionally, EVA is unstable at highextrusion temperatures, notably of the order of 200 to 220° C.

None of the above documents teaches nor suggests the present invention.

SUMMARY OF THE INVENTION

The invention provides a composition comprising, by weight:

(i) from 1 to 99% of a metallocene catalyzed ethylene/alpha-olefincopolymer; and

(ii) from 99 to 1% of a radically catalyzed ethylene/alkyl(meth)acrylate copolymer, the ratio of their secant moduli being greaterthan 1.

In one embodiment, the radically catalyzed ethylene/alkyl (meth)acrylatecopolymer content is comprised between 5 and 25%.

Preferably, the flexural modulus of each copolymer is comprised between10 and 100 Mpa.

The ratio of their flexural moduli is advantageously greater than 1.

The metallocene catalyzed ethylene/alpha-olefin copolymer has apolydispersity index of for example between 2 and 5, and preferablybetween 2 and 3.

The metallocene catalyzed ethylene/alpha-olefin copolymer has a densityfor example comprised between 0.905 and 0.880 and preferably between0.900 and 0.880 g/cm³.

The metallocene catalyzed ethylene/alpha-olefin copolymer has an MFIcomprised for example between 0.5 and 10 dg/min, and preferably between0.8 and 5 dg/min.

The radically catalyzed ethylene/alkyl (meth)acrylate copolymer forexample comprises, by weight based on the weight of said copolymer, from5 to 40% of a C₁ to C₈ alkyl (meth)acrylate.

The radically catalyzed ethylene/alkyl (meth)acrylate copolymer has anMFI typically comprised between 0.3 and 10 dg/min.

The invention also provides a film obtained from a composition accordingto the invention, preferably extruded.

The invention particularly provides a stretchable cling film obtainedfrom the composition of the invention.

The invention also provides a process for extruding a compositionaccording to the invention, comprising extruding said composition at atemperature greater than or equal to 200° C., for example between 210and 230° C., in particular for the production of film.

The invention will now be described in more detail below.

DETAIL DESCRIPTION OF THE INVENTION

The term “metallocene catalyzed ethylene/alpha-olefin copolymer” as usedherein refers to such copolymers obtained by metallocene catalysis andthe expressions “plastomers” or “metallocene catalyzed ethylenecopolymer” are equivalent in the description below.

It will be recalled that such metallocene catalysis is a single-sitecatalysis implementing a catalyst generally constituted by a metal atombetween two alkyl cycles bonded to the metal. For the metal, all themetals of transition groups IVA, VA and VIA can be used as well as thelanthanides. Preferred metals are hafnium, zirconium and titanium. Forthe alkyl cycle, one would generally use cyclopentadiene. Optionally, aco-catalyst or activator such as for example an aluminoxane, such asmethylaluminoxane (MAO) will be used. For other details of suchcatalysis, the person skilled in the art is referred to classical worksin the field.

For the alpha-olefin, any alpha-olefin having 3 to 12 carbon atoms,preferably 3 to 8 carbon atoms can be used. Examples of alpha-olefin arepropylene, butene, hexene and octene. A preferred alpha-olefin isoctene. The alpha-olefin proportion in the plastomer can extend up to40% by weight and varies conventionally between 10 and 35% by weight,for example between 10 and 30%.

In the case of a stretchable cling film, one for example can use octeneas alpha-olefin, the proportion being comprised for example notablybetween 20 and 25%.

These plastomers of the invention are homogeneous in composition.

The density of these metallocene catalyzed copolymers is less than 0.900g/cm³, generally comprised between 0.900 and 0.875 g/cm³, preferablybetween 0.900 and 0.880 g/cm³.

The polydispersity index of these plastomers is low, generally comprisedbetween 2 and 5, preferably between 2 and 3. The MFI (molten flow indexas measured by ASTM D 1238-73) is generally comprised between 0.5 and 10dg/min, preferably between 0.8 and 5 dg/min.

These plastomers are substantially linear.

The flexural modulus of such plastomers is preferably comprised between10 and 100 Mpa; for example between 10 and 50 Mpa.

Mixtures of plastomers are also envisaged.

Such plastomers are available commercially from Dow and Exxon under therespective names of Affinity and Exact.

The term “radically catalyzed ethylene/alkyl (meth)acrylate copolymer”designates such copolymers comprising, by weight with respect to theweight of said polymer, up to 60% by weight of alkyl (meth)acrylateobtained by synthesis with free radical initiator, the terms used herein“ethylene/(meth)acrylate copolymer” and “EAA copolymer” beingequivalent.

These EAA copolymers are generally obtained in a high pressure processand generally exhibit a wide molecular distribution and long branchingdistribution (i.e. a branch having a number of monomer segments of thesame order as that of the main chain). Examples and methods of preparingsuch EAA copolymers are for example given in U.S. Pat. Nos. 4,617,366and 5,543,233, incorporated herein by reference.

The (meth)acrylate weight content with respect to the EAA copolymerweight is generally comprised between 1 and 60%, in particular between 5and 40%.

The expression alkyl (meth)acrylate refers to linear, branched or cyclicalkyl methacrylate and acrylate having from 1 to 12, preferably 1 to 8carbon atoms, for example methyl, ethyl, butyl and 2-ethylhexyl.Specific examples of EAA copolymer are methyl methacrylate, methylacrylate, ethyl acrylate, butyl acrylate.

The MFI index of such EAA copolymers is generally comprised between 0.1and 400 dg/min, for example between 0.3 and 10 dg/min.

Other monomers can optionally be present in the EAA copolymers, providedthe final properties are not affected. Examples of such termonomers aresaturated carboxylic acid, vinylic esters, maleic anhydride and glycidyl(meth)acrylate. This termonomer can be present in an amount of, forexample, up to 10% by weight, based on the weight of said EAA copolymer,and can be grafted or terpolymerized.

As the thermal degradation temperature of these EAA copolymers is high,habitual plastomer transformation temperatures can be employed withoutany risk of degrading the EAA copolymers.

The flexural modulus of such EAA copolymers is preferably comprisedbetween 10 and 100 Mpa; for example between 10 and 50 Mpa.

Mixtures of EAA copolymers are also envisaged.

In the case of stretchable cling films, a preferred EAA comprises amethylacrylate and/or has an MFI comprised between 3 and 10 dg/minand/or comprises between 20 and 35% by weight acrylate.

Such EAA copolymers are available commercially from Elf Atochem underthe brand name Lotryl®.

One particular embodiment corresponds to the case where the ratio:$\frac{\text{flexural modulus of plastomer}}{\text{flexural modulus of EAA copolymer}}$

is greater than 1 and for example comprised between 1 and 3.

Such a ratio is for example useful for “bulky” objects obtained fromcompositions of the invention.

Another particular embodiment corresponds to the case where the ratio:$\frac{\text{Secant modulus of the plastomer}}{\text{Secant modulus of EAA copolymer}}$

is greater than 1 and for example, is comprised between 1 and 3.

Such a ratio is useful for example for films obtained from compositionsof the invention.

It will be clear that other polymers can also be added to thecompositions according to the invention, in amounts that do not impairthe sought-after properties and which are conventional for the personskilled in the art.

It is equally clear that conventional additives and supplements can beadded to the mixtures according to the invention in conventional amountsfor the person skilled in the art. Examples of such additives areanti-UV, anti-oxidizing agents, pigments, fillers such as silica,fibers, etc.

The invention also provides objects obtained from such mixtures, andnotably films. The thickness of the film is conventional comprised forexample between 10 and 500 μm. The films are manufactured inconventional plant for PE, LDPE, etc.

The films according to the invention comprise at least one layerobtained from a composition according to the invention.

According to one alternative embodiment, the films according to theinvention comprise a cling layer and are stretchable cling films. Inthis case, the cling layer according to the invention comprisessufficient EAA copolymer, advantageously from 5 to 50%, EAA polymer inwhich the acrylate comonomer content is advantageously comprised between10 and 35%, preferably between 20 and 35%.

According to another alternative embodiment, the films according to theinvention comprise a cling layer obtained from the composition accordingto the invention, and a slip layer. This slip layer can be obtained froma polyolefin such as a polypropylene or polyethylene (LLDPE, LDPE,metallocene). This slip layer can also contain anti-bonding and/orsliding additives. In the film, the cling layer represents from 5 to95%, preferably 5 to 35%, advantageously 10 to 20% of the combinedthickness of the cling and slip layers.

Other layers may be present for obtaining multi-layer films.

The mixtures according to the invention can be prepared by anyconventional process, notably compounding, using, for example, asingle-screw kneading profile extruder, twin-screw extruders, internalmixers, cylinder mixers, etc. The mixtures can also be obtained directlywith transformation extruders, extruded in the form of tubes, films,shaped parts, on injection press, etc. The operating conditions are theones conventional for PE, LDPE, etc.

In particular, it is possible to extrude the compositions of theinvention at temperatures greater than or equal to 200° C., for examplebetween 210 and 230° C., without any danger of deteriorating theproducts.

The invention consequently makes it possible (i) to modify metallocenecatalyzed plastomers to impart processability suitableness to them,notably for reducing specific energy and improving extrudate stabilityand, in parallel (ii) modification of the EAA copolymers to improvetheir mechanical and optical properties.

The following examples illustrate the invention without limiting it.

EXAMPLES

In these examples, the mixtures were obtained on a tube extruder fittedwith a three-zone screw with a mixture of the type for radical LDPE, andof 45 mm diameter. Temperature profile is increasing, and terminates at230° C., screw speed being 100 rpm for extrusion of the controls and thecompositions according to the invention. All the sleeves are stretchedto a thickness of 500 μm with a blowing ratio of 2.

The compositions were obtained from the following copolymers:

A1 ethylene/octene copolymer of bulk composition 88/12, obtained bymetallocene catalysis, of density 0.902 g/cm³, MFI 1.0 dg/min,corresponding to the copolymer in the second line of table 1, page 6, ofinternational application WO-A-9507314.

A2 ethylene/octene copolymer of bulk composition 86/14, obtained bymetallocene catalysis, of density 0.895 g/cm³, of MFI 1.6 dg/min.

B ethylene/methyl acrylate copolymer of MFI 2 dg/min and bulk ratioamount of methyl acrylate of 16.5% (corresponding to a molar percentageof 6%).

C ethylene/methyl acrylate copolymer of MFI 0.3 dg/min and bulk methylacrylate percentage of 14% (corresponding to molar percentage of 5%).

D ethylene/methyl acrylate copolymer of MFI 7 dg/min and bulk methylacrylate percentage of 28%.

The following characteristics were determined on the examples below:

Specific energy of the material in kWh/kg corresponding to motor powerof the extruder with respect to material throughput.

Haze expressed as percentage of light scattered, measured as per ASTM D1003.

Tear resistance measured by the Elmendorf (ASTM D 1922) method in themachine direction (MD) and transverse direction (TD) expressed in g/50μm.

Impact resistance measured by the Dart (ASTM D 1709) method expressed ing/50 μm.

Secant modulus (or modulus at 1% elongation) measured according toASTM-D-882, expressed in Mpa.

Comparative Example A

(ECA)

Copolymer A1 was extruded alone. Extrusion throughput was less than 34kg/h and an absence of stability of the extrudate and a specific energyof the polymer leading to the motor absorbing a power very close to theacceptable limit were noted.

This example was repeated with copolymer A2; the same results wereobtained.

Comparative Example B

(ECB)

Copolymer B was extruded alone. Extrusion was stable at a throughput of34 kg/h and it was noted that the motor was absorbing a powercorresponding to around 50% of the maximum.

Comparative Example C

(ECC)

Copolymer C was extruded alone. Extrusion was stable at a throughput of35 kg/h and it was noted that the motor was absorbing a powercorresponding to around 65% of the maximum.

Example 1

A mixture of 80% by weight copolymer A1 and 20% by weight of copolymer Bwas prepared. A stable extrudate was obtained with an increase inthroughput of 10%. The film had good optical properties and improvedtear resistance compared to films from A1 and B alone.

Example 2

80% by weight copolymer A1 were mixed with 20% by weight copolymer C. Astable extrudate was obtained with an increase in throughput of 10%.

Example 3

60% by weight copolymer A1 were mixed with 40% by weight copolymer B. Astable extrudate was obtained with an increase in throughput of 20%.

Example 4

60% by weight copolymer A1 were mixed with 40% by weight copolymer C. Astable extrudate was obtained with an increase in throughput of 20%.

Examples 1 to 4 were repeated with copolymer A2; similar results wereobtained.

Example 5

40% by weight copolymer A1 were mixed with 60% by weight copolymer B.Extrusion remained stable. An improvement in impact resistance, tearresistance and haze were noted.

Example 6

40% by weight A1 were mixed with 60% by weight copolymer C. Extrusionremained stable. An improvement in impact resistance, tear resistanceand haze were noted.

Example 7

20% by weight copolymer A1 were mixed with 80% by weight copolymer B.Extrusion remained stable. An improvement in impact resistance wasnoted.

Example 8

20% by weight copolymer A1 were mixed with 80% by weight copolymer B.Extrusion remained stable. An improvement in impact resistance, tearresistance and haze were noted.

The results are summarized in the table below in which (2) means thatthe example is the one corresponding to copolymer A2. A reading of theresults makes it possible to conclude that the mixtures according to theinvention offer good mechanical and optical properties while allowingimproved processability.

Example 9

60% by weight copolymer A1 were mixed with 40% by weight copolymer D.The properties of the resulting film were determined. This film is astretchable cling film.

Example 10

A twin-layer product was prepared, the cling layer of which was thelayer of the preceding example and the slip layer of which was obtainedfrom copolymer A1, the cling layer making up 18% of the overallthickness of the final film.

Examples 9 and 10 were repeated with copolymer A2; the same results wereobtained.

Example 11

Example 9 was repeated this time with a copolymer of density 0.891,comprising 24% by weight octene. A film having excellent clingproperties was obtained.

Obviously, the present invention is not limited to the embodimentsindicated, but may be subject to numerous variations readily accessibleto those skilled in the art.

Specific Impact Composition (%) energy resistance Tear resistance (g)Secant Ex. A1 A2 B C (kWh/g) Haze (%) (g) MD TD module ECA 100 0.351.6 >840 688 779 26 ECA (2) 100 0.35 1.9 >840 580 1044 28.2 ECB 100 0.168.7 373 253 302 18.4 ECC 100 0.23 25.3 571 165 360 16.8 1 80 20 0.323.1 >840 790 958 22.3 1 (2) 80 20 0.32 3.3 >840 691 1078 24.3 2 80 200.33 6.8 >840 661 749 18.5 2 (2) 80 20 0.33 7.0 >840 606 886 19.5 3 6040 0.22 4.6 >840 522 674 22.8 3 (2) 60 40 0.22 4.9 >840 488 722 23.9 460 40 0.31 10.5 >840 563 728 22.4 4 (2) 60 40 0.31 11.8 >840 531 82824.1 5 40 60 0.20 9 >840 330 467 18.8 6 40 60 0.27 12.3 >840 350 51719.4 7 20 80 0.18 13.1 >840 219 282 29.4 8 20 80 0.23 17.8 727 190 37928

What is claimed is:
 1. A stretchable cling film, comprising at least onecling layer obtained from a composition comprising, by weight: (i) from50 to 95% of a metallocene catalyzed ethylene/alpha-olefin copolymer;and (ii) from 50 to 5% of a radically catalyzed ethylene/alkyl(meth)acrylate copolymer, the ratio of their secant moduli being greaterthan
 1. 2. The film according to claim 1, in which the metallocenecatalyzed ethylene/alpha-olefin copolymer has a polydispersity indexbetween 2 and
 5. 3. The film according to claim 1, in which themetallocene catalyzed ethylene/alpha-olefin copolymer has a density ofbetween 0.900 and 0.880 g/cm³.
 4. The film according to claim 1, inwhich the metallocene catalyzed ethylene/alpha-olefin copolymercomprises an alpha-olefin proportion between 10 and 30% by weight. 5.The film according to claim 1, in which the metallocene catalyzedethylene/alpha-olefin copolymer is an ethylene/octene copolymer.
 6. Thefilm according to claim 1, in which the radically catalyzedethylene/alkyl (meth)acrylate copolymer comprises by weight based on thecopolymer weight, from 5 to 40% of a C₁ to C₈ alkyl (meth)acrylate. 7.The film according to claim 1, in which the radically catalyzedethylene/alkyl (meth)acrylate copolymer has an MFI of between 0.3 and 10dg/min.
 8. The film according to claim 1, additionally comprising a sliplayer.
 9. The film according to claim 8, in which said slip layercomprises a polyolefin.
 10. The film according to claim 8, in which thecling layer represents from 5 to 35% of the combined thickness of thecling and slip layers.
 11. A process for preparing a film according toclaim 1, comprising extruding said composition at a temperature greaterthan or equal to 200° C.
 12. A stretchable cling film comprising atleast one cling layer obtained from a composition comprising, by weight:(i) from 50 to 95% of a metallocene catalyzed ethylene/alpha-olefincopolymer; and (ii) from 50 to 5% of a radically catalyzedethylene/alkyl (meth)acrylate copolymer, the ratio of their secantmoduli being greater than 1, and wherein the metallocene catalyzedethylene/alpha-olefin copolymer is an ethylene/octene copolymercomprising an octene proportion between 10 and 30% by weight; and theradically catalyzed ethylene/alkyl (meth)acrylate copolymer comprises byweight based on the copolymer weight, from 5 to 40% of a C₁ to C₈ alkyl(meth)acrylate.
 13. The film according to claim 12, in which themetallocene catalyzed ethylene/alpha-olefin copolymer has a density ofbetween 0.900 and 0.880 g/cm³.
 14. The film according to claim 12,additionally comprising a slip layer.
 15. The film according to claim14, in which said slip layer comprises a polyolefin.
 16. The filmaccording to claim 14, in which the cling layer represents from 5 to 35%of the combined thickness of the cling and slip layers.
 17. A processfor preparing a film according to claim 12, comprising extruding saidcomposition at a temperature greater than or equal to 200° C.